targets/wasi: remove --export-dynamic linker flag

Exporting symbols seems to embed them in the WASM exports section which
causes wasmtime to fail: bytecodealliance/wasmtime#2587
As a workaround, it is possible to specify the `--allow-unknown-exports`
flag on wasmtime.
But as discussed in the above linked issue, this seems to only be a
workaround. For the Rust compiler the fix was to remove the
`--export-dynamic` linker flag when targeting `wasm32-wasi`:
rust-lang/rust#81255
Which is waht this commit does for Tinygo too.

targets/wasi.json

@@ -11,7 +11,6 @@
 	"ldflags": [
 		"--allow-undefined",
 		"--stack-first",
-		"--export-dynamic",
 		"--no-demangle"
 	],
 	"emulator":      ["wasmtime"],